1. Field of the Invention
This invention relates to the repair of refractory brick walls used in high temperature installations, and more particularly to the repair of such walls by removing and replacing damaged brick without requiring cooling of the wall to ambient temperature.
2. Description of the Prior Art
Substnaital improvements have been made, and continue to be made, in refractory brick of the type employed in high temperature applications such as in industrial furnaces and coke ovens. As a result, the strength and resistance to thermal shock, and consequently the life expectancy of walls constructed from such brick, have been greatly increased. Nevertheless, maintenance and repair of such walls continues to present severe problems, both from the standpoint of making a satisfactory repair and from interruption of or interference with production during the repair.
The invention is particularly well adapted for repairing refractory brick liner walls of a coke oven and will be described herein with reference to coke oven repair; however, it should be understood that the invention may be employed in repairing other high temperature brick walls and is not limited to use in coke ovens.
Coke ovens are normally constructed of refractory silica brick which maintain relatively high strength even at the extreme temperatures encountered in the coking operation. Such ovens may have an overall life expectancy of 40 years or more, but may nevertheless require repair after only a few years of operation. Spalling of the refractory brick in the lining wall may commence for various reasons, including small cracks resulting, for example, from foundation settling, uneven expansion during heat-up or cool-down, air leaks, thermal shock and/or repeated thermal cycling during operation. The inclusion of foreign material in a coal charge can also produce "hot spots" which damage a local area. Once spalling has commenced, it can progress both to adjacent brick and more deeply into the wall until it interferes with pushing of the coke which, again, can produce more damage. Unless properly repaired, the damage can progress through the wall liner to the heating flues.
Since coke ovens are normally constructed in batteries each consiting of a large number of ovens extending in side-by-side relation with common walls between adjacent ovens, repair of an individual oven wall liner can not, from a practical standpoint, be accomplished by cooling only the oven needing repair since flues in the common wall are required to heat the adjacent ovens. Further, any attempt to cool one oven in a battery to a temperature that would enable workmen to enter and make repairs, even if adjacent ovens were partially cooled, would result in severe stresses due to shrinking and could cause substantial damage both to the oven being repaired and to adjacent ovens. Accordingly, it has long been the practice to repair coke oven liner walls by applying a temporary patch over the dampaged area using a gunning or spraying technique wherein refractory aggregate is applied either as a slurry or in a "dry" gunning mixture which is sprayed or thrown directly onto the hot oven wall. The difficulties encountered in applying such patching material are well-known to those skilled in the art and are generally discussed, for example, in U.S. Pat. No. 3,413,385. Particular difficulty is encountered in repairing oven liner walls by the gunning process in areas which can not conveniently be reached through an open door by repairmen, protected by a heat shield, standing outside the oven.
Although various techniques and procedures have been developed for repairing hot refractory walls utilizing a gunning process, the results have not been satisfactory and generally have produced only a temporary repair which must be repeated at frequent intervals. Further, the adverse conditions under which such repair material is applied makes complete control of the application virtually impossible; material sagging and overspray frequently occur, producing rough and uneven wall surfaces which can interfere with pushing and further shorten the life of the repair. Eventually damage progresses until it can not be repaired by gunning and it is necessary to shut down and replace the complete wall.
Particular difficulty is encountered in making repairs to coke oven walls where the damage has progressed through the wall liner into a flue in the oven wall. If only a small opening or crack has penetrated to the flue, repair can sometimes be effected by a gunning process, although some of the sprayed refractory material will frequently pass through the opening and drop into the flue. Larger openings, however, cannot be successfully repaired in this manner.
It is, accordingly, the primary object of the present invention to provide an improved method for repairing refractory brick walls.
Another object is to provide an improved method of effecting permanent repairs of coke oven wall liners without requiring adjacent ovens to be shut down.
Another object of the invention is to provide a method of repairing a coke oven wall liner by removing and replacing damaged brick while the wall is maintained at a temperature sufficiently high to avoid damage resulting from shrinkage.
Another object of the invention is to provide a method of repairing a hot refractory brick wall by removing and replacing damaged brick wherein workers wearing protective clothing work in ovens having an internal surface temperature of up to 500.degree. F. or higher and internal temperatures substantially above 500.degree. F.
In the attainment of the foregoing and other objects and advantages, an important feature of the present invention resides in making repairs to refractory brick walls of a coke oven chamber while maintaining the walls at a temperature sufficiently high to avoid damage resulting from cooling. To accomplish this, the oven doors are removed, leaving the oven open to the atmosphere for a period of about eight hours, or until the surface temperature of the brick wall liners reaches approximately 500.degree. F. During this time, the heat in the flues in the walls on each side of the oven is reduced preferably to about 1500.degree. F. Surprisingly, it has been discovered that silica refractory brick which have been used as oven liner walls for extended periods shrink very little with this reduction in temperature so that essentially no damage due to thermal contraction is encountered. By controlling the temperature in the flues inside the walls being repaired and in the adjacent ovens the surface temperature of the walls inside the oven chamber can be maintained at the desired level for a time sufficient to complete the necessary repairs.
When the oven to be repaired reaches the desired reduced temperature, workers wearing protective clothing enter the open oven chamber to remove the brick from the damaged section of the wall liner. This is accomplished by initially cutting around the damaged section, using a suitable saw preferably powered by compressed air, and with the saw cutting completely through the brick of the liner wall and into any flue chambers located behind the damaged area. After cutting around the damaged area, using only horizontal cuts along an original mortar line and vertical cuts extending along mortar lines where possible, the damaged brick are removed using suitable tools. In the vertical portions of the wall between adjacent flues, brick are carefully removed along mortar joints to enable replacement with new brick which will tie directly into the existing structure and the wall liner repair.
After the damaged brick are completely removed, any exposed flues are cleaned to remove any refractory material which may have fallen either during operation of the oven or during removal of the damaged area. Before starting the repair, fuel is blocked from the flues in the damage area; however, heat is applied at a reduced level to the wall through flues which will not be exposed through the removed wall sections.
After completely removing the damaged brick and cleaning the flues and repair area, the wall portion is rebuilt using brick having a coefficient of thermal expansion compatible with the wall at the temperature at which repair is made. Repair may be accomplished by workers carrying brick, having mortar applied from outside the oven and carefully reconstructing the removed portion of the wall. Upon completion of the repair, the oven can be closed and reheating commenced immediately to bring the coking chamber back up to operating temperature. When the desired temperature is reached, the oven may be charged and operated in the normal manner since the permanently installed repair has sufficient strength to withstand stresses of the normal coking operation.
Since the coking chamber of a regenerative coking oven is relatively narrow, working within the chamber necessarily entails considerable contact with the hot refractory brick wall which tends to quickly damage the protective clothing. In order to minimize such damage and to thereby provide an increased element of protection for the workers, a smooth surface tile may be applied to the inner surface of the liner wall in the undamaged areas before commencing the repair operation. The individual tiles may be relatively large and be adhesively bonded directly to the refractory brick wall surface. By applying adhesive outside the oven, the tiles can be carried into the oven and installed very quickly. The tile and adhesive are able to withstand the reduced temperature of the oven but are consumed during a coking operation so that contamination of coke by tile which are left in place at the completion of the repair operation is avoided. Alternatively, a heat insulating curtain may be suspended along the wall surfaces as from a cable passed through the oven, with the curtain and cable being removed at the completion of the repair operation.